Hiya, I'm new here. I was wondering which encoder and what settings I should use to create a MPEG-4 compliant AAC that I can mux with my video to be able to play on (future) standalone players?

Will there be much difference if I transcode a DVD AC3 file into AAC? What should I do to minimise the quality loss? Can AAC do 5.1 channel sound?

Please help, thanks!

You can use Psytel AACenc. I would suggest creating an AAC LC with ADTS header. If the multiplexer outputs some error because of the header, try creating a RAW AAC LC (switch -nh )



Yes. Psytel AACenc creates 5.1 AAC file, and you can use the -lfe switch to create the LFE channel.

I don't know about transcoding. Usually is bad but, if you want to shrink the bitrate of the stream, it´s much better than using AC3 for this purpose. (Even Dolby agrees that AAC is superior to AC3 altough, according to Ivan, they "play with the words")

Regards;

Roberto.

Hmm, ok. Cos I'm trying to make some DVDs into MPEG-4 CD-rs.

Thanks for the information Roberto. I'm always interested in 5.1 technology.

@Shiki
Is it possible for you to report back on your experience? I'm very much interested and plan to do some testing myself.

Sure, but I'm waiting for the new XviD with B-frames support before I continue testing... Can MPEG-4 video files use AC3 btw?

I'm drooling while waiting on the B Frames in Xvid :-)

I've only seen vague reports of people muxing MP3 or AAC into MP4. I've never heard of anyone getting AC3 to work with MP4 though.

I'm in on this, too. I am just waiting for the xcard to arrive so I can see what that will let me outut-I'm kind of hoping it will do xvid/ac3, but the 5.1aac sounds interesting, too.

Let's remember MP4 is a container format. So, pretty much everything can be added - provided you have the decoding filter. Even Cinepak with VQF

If course, in this case, it wouldn't be ISO compatible - I.E: ISO-only players wouldn't play the non-ISO content.

Regards;

Roberto.

Hmm, cool. So you can use VBR mp3 too? Then I can just convert all my avis to mp4.

Does this mean that XviD/.ac3 will be supported by the ISO/standalone players?

XviD IS MPEG4 video simple profile. No more. You can rename it to DivX, or multiplex in a MP4 file, and it will work fine.

Regarding AC3 (Or any other format: OGG, MPC...), I don't think so, and I don't hope so. I don't think so, because AC3 is not part of MPEG4 standard. And I don't hope so because AAC is better than AC3.

How so? I hope you know me well enough to know I am not being antagonistic, merely inquisitive. rjamorim, you seem to be a big proponent of the .aac format, and I am curious as to the specific reasons why. Thanks for the indulgence...

Up to this point, I thought that leavng .ac3 audio alone was the way to go. Does ISO MPEG-4 have a specified audio format, like SVCD(mpeg-2) format has .mp2? Does MPEG-4 only apply to the video? If it applies to audio (and .ac3 is out, and .aac is in) what about the .mpc and .ogg audio formats? When products (like sigma's xcard) say MPEG-4 compliant, is there only one audio/video format that works, or are these products simply processing the video (the MPEG-4 part) and passing through the audio to the soundcard?

I apologize for my ignorance; thanks for any input.

This is true.

I think rjamorim was referring to AAC as being better than AC3 when encoding from the same source material, not in terms of transcoding. But I have never made a direct comparison between AC3 and AAC so I also await rjamorim's response

Regarding AAC being better than AC3, I trust Ivan's words in this matter. You can see his post here, around the middle of the thread.

Regarding why I prefer AAC rather than Musepack or Vorbis:

1. - It's an ISO standard, and the MPEG4 official audio format. So, if, in the future, I decide to multiplex the audio in a MP4 strem, It'll be piece of cake.

2. - The quality is great at the bitrates I use (160 - 200). I don't need more than that for the kinds of music I enjoy.

3. - It already has Hardware support, and I keep dreaming on buying an Expanium someday.



Yes. And this specified audio format is AAC. (Among others: CELP, TwinVQ, Midi...)



I would have to take a look at the card specs, but I would bet that it focuses in video decoding, and the audio decoding is mainly (If not completely) processed by the CPU.

As example, there's the case of DVD hardware accelerators. The main tasks they perform are iDCT (which provides about 40% decoding acceleration) and Motion Compensation (30% decoding acceleration). Most of the audio decoding (AC3, DTS...) is performed by the CPU, as well as 30% of the video decoding.



No problem.



That's It.
And I mentioned something like that, when said that, to reduce the size of an 5.1 audio stream, it would be better to transcode to 5.1 AAC than to reencode in AC3 in a lower bitrate.

Regards;

Roberto.

Just found it:
http://www.sigmadesigns.com/products/xcard...cifications.htm

It seems it decodes MPEG audio, but not full 5.1 AC3 or DTS. (AC3, only downmixing to 2 channels)

Regards;

Roberto.

Thanks for clarifying-I will read the referenced thread when I get home from work...

Hopefully with the xcard, like with current h+, the .ac3 will pass through to the receiver, not requiring any processing at all. I am assuming that .aac cannot be passed through in this way-I don't think the surround receiver will not recognize 5.1 .aac audio (in which case the audio woould have to e processed by CPU)...

I am asking because I am starting to put together MPEG-4 clips to test on the new card when it arrives (after being shipped at the end if this month)...

Thanks again for the help.

I don't think the Xcard will handle 5.1 AAC audio. If you look at the MPEG-4 chip used, it is supposed to support profile Level 2 MPEG-4 audio which can only handle 2-channels I believe. Maybe some other company will design an MPEG-4 chip in the future that can handle 5.1 AAC...